Summary A continuous challenge for both single cells and multicellular organisms is that the availability of nutrients is fluctuating constantly. This is particularly the case for cancer cells in solid tumors or exposed to different stromal environments. Hence, cells must sense the amount of nutrients in the environment to coordinate energy-consuming anabolic reactions with energy-producing catabolic reactions. This task is largely carried out by mTOR complex 1 (mTORC1), a protein kinase complex that senses various environmental cues and coordinates anabolic and catabolic processes to regulate cellular homeostasis. mTORC1 is activated only when amino acids, energy sources, oxygen and growth factor levels are sufficient. Under these conditions mTORC1 promotes cell growth by boosting protein, lipid and nucleotide synthesis. However, whereas many of the key players involved in growth factor signaling to mTORC1 have been characterized, much less is understood about how mTORC1 senses amino acids. It is also unclear how different cancer cell-associated mutations provide tumor cells with the ability to optimize usage of these regulatory components or find ways to overcome deficiencies in these mTORC1 regulators. Additionally, once activated it is still a mystery how mTORC1 regulates and coordinates the many processes required to promote cell growth, proliferation, migration, and survival, and how the altered signaling in cancer cells leads to resistance to current mTORC1 therapies with rapamycin (an FDA approved mTORC1 inhibitor). Along these lines it remains unclear how mTORC1 can regulate the variety of biological processes associated with cancer. To better understand mTORC1 signaling, we can now combine our mTORC1 RNAi screens, and phosphoproteome, interactome, metabolome and gene expression data sets, to support our efforts. In this proposal we have outlined several goals based on this new information, our published work and the extensive experience of my lab, that support our long-term goals of defining mTORC1 regulation and signaling, and for revealing new insight to support efforts to kill cancer cells with activated mTORC1 signaling. Our scientific discoveries and experience have now led us to investigate a novel mechanism for responding to amino acid availability (aim 1), a new pathway for regulating nuclear GSK3 signaling and gene expression of targets linked to biological processes hijacked by cancer cells (aims 2 & 3), and novel mechanisms associated with mRNA biogenesis as a means of changing gene expression and increasing protein diversity (aim 4). In conclusion, there's a critical need for a greater understanding of the molecular basis of mTORC1 regulation and signaling, and its links to processes associated with cell growth, migration/invasion, survival and drug resistance. Our expectations are that successful completion of the proposed work will impact cancer biology/physiology and therapy through the identification of new therapeutic targets and biomarkers that will improve detection and elimination of cancer cells with unregulated mTORC1 signaling, estimated to occur in 70-80% of human cancers.